Electromagnetic motor



Feb. 6, 1962 R. STEINER ELECTROMAGNETIC MOTOR 2 SheetsSheet 1 Filed Oct. 20, 1958 INVENTOR:

RUDOLF STEINER remote from the rotatable armature.

electromagnetic motor structures normally employ at least one mechanical spring to return the armature to its United States Patent 0 "ice 3,020,425 r ELECTROMAGNETIC MOTOR Rudolf Steiner, 17215 Valerio St., Van Nuys, Califi, as-

siguor of one-half to Eugene D. Kilmer, Los Angeles,

Calif.

Filed Oct. 20, 1958, Ser. No. 768,130 18 Claims. (Cl. 310-20) This invention relates generally to electromagnetic devices and more particularly to an improved electrical coil and core arrangement and combinations thereof with various other components to provide improved relays, stepper type motors, circuit breakers, and other electromagnetically controlled devices.

Most, if not all known devices of this variety comprise, in addition to the required operational air gap in the core, several other air gaps because of the respective design, construction and assembly methods. These nonoperational air gaps may be small in size per se or by com parison; however, they are either responsible for additional ampere-turns needed for the energizing coil, or for operational losses such as magnetic leakage fluxes, or for any unfavorable combination of those deficiencies. The operative part of those devices, the armature, is usually hinged at one point of the magneticstructure this introducing, atone end, a movable union having a large magnetic reluctance and, at the other end a seating arrangement between the two surfaces of the magnetic structure which, considering recognized manufacturing methods, will result in an abutment of parts having a specific, nonopcrational air gap constituting another large magnetic reluctance. Disregarding the other air gaps existing between unions of nonmovable assembly parts of the conventional magnetic structure types, it appears to be fair to state that these two major magnetic reluctances and the magnetic leakage conditions caused by them account for a significant portion not only of the excessive but of all ampere-turns needed for the'energizing of an electromagnetic motor. The aforesaid conventional magneticcirucit structures allow normally for but one energizing-coil location, i.e., upon one stationary leg of the magnetic structure and at that considerably These traditional rest position upon the cessation of the electromagnetic energizing force of the coil. Each such return Spring usually necessitates several additional assembly parts which need to be incorporated into each of the ineificient' in addition thereto, the mechanical return spring, resulting in an extremely straightforward and compact design of optimum efiiciency and performance, and having a minimum of individual, economically-sized assembly parts. i

Both the construction and operation of the new electr'omagnetic motor evolve about the fundamental electromagnetic principle that the magnetic field intensity of the magnetic leakage flux reduces to zero only if the air gap length is reduced to zero. Because the length of an operational air gap cannot normally equal zero and will, theoretically, not equal zero even if it is'completely closed, the energizing of the magnetic circuit and the suppression of magnetic leakage must be exercised, in compliance with another elementary law of physics, from of design,

the location where the magnetic energy is concentrated and where, consequently, the magnetomotive force and the ampere-turns, respectively, are immediately required for the energization of each specific magnetic circuit portion rather than arranged, cumulatively, at an arbitrary point along the magnetic circuit or where the convenience manufacture or assembly may dictate. Whereas the aforesaid law requires that each magneticcircuit portion so long as its magnetic characteristic varies from any of the other magnetic circuitportion, be magnetically energized by an individual and correlated energizing coil, specific allowances may be in order for a magnetic circuit constructed of a high-permeability material, particularly of the grain-oriented variety, having but one, operational, air gap. In such a case, the reluctance of the air gap will be, by a factor of several thousands, greater than that of the iron portion and, consequently, the overwhelming share of the magnetic energy will be located within the space occupied by the air gap. It will then be permissible to disregard the energy required for the magnetization of the iron portionof the magnetic circuit, and to calculate the ampere-turns required for the energization of the operational, air gap only and to arrange the coil where it is actually needed, i.e., across and encompassing the air gap. If the iron portion of the g a spring, obviating the formerly required mechanical armature return springtogether with its assembly parts. A further advantage follows from the arrangement of the coil at the point of greatest need for energy because the magnetic leakage circuit of the magnetic circuit is thereby, for practical purposes, eliminated, resulting in a particularly effective response of the magnetic circuit and in an energizing coilhaving considerably smaller dimensions than conventional designs. This, consequently, amounts to substantial savings in materials, overall weight and cost of the magnetic circuitand the entire device, respectively. These factors are of decisive importance when large quantities of devices equipped with these electromagnetic motors are used to keep both the total weight and the electric power demand of the equipment to a minimum.

On the basis of the foregoing, an electromagnetic rn'otor having the described properties and qualifications,- respectively, may be utilized for various applications closely related to each other with regard to the opera tional modes yet not necessarily concerning the respective end. uses. Such an electromagnetic motor may function (1) as a genuine motor, advancing physically. or moving mechanical or electr'o-mechanical parts, or

(2) as an actuator of electromagnetic relays of various denominations, or (3) as an electromagnetic solenoid, or (4) as a sensing and releasing means of electric monitoring or protection devices such as circuit breakers or (5),

as a vibrator causing electric, acoustic or visual effects,

Patented Feb; 6, 1962 front elevation, another possible ratchet arrangement for use with the basic electromagnetic motor; FIG. illustrates, in front elevation and cross section, one possible construction of an electromagnetic relay utilizing said electromagnetic motor as the actuating means; FIG. 6 is a schematic plan view of the relay header showing the arrangement of the movable and stationary contacts; FIG. 7 presents, in front elevation and cross section, one possible design of a solenoid employing said electromagnetic motor; FIG. 8 represents, in front elevation and cross section, specific details of a push-type solenoid utilizing the subject electromagnetic motor; FIG. 9 indicates, schematically and substantially in front elevation, an electromagnetic motor of the subject variety operating as the sensing and release means of an electric circiut breaker; and FIG. 10 illustrates, schematically and essentially in front elevation, the subject electromagnetic motor functioning as an electromagnetic vibrator.

Referring now to the drawing, wherein like numerals designate like or identical parts, and particularly to FIGURES l and 2, the generic electromagnetic motor is presented, in the de-energized position comprising a core 10 of ferrous laminations 12, which constitutes the magnetic circuit for the energizing coil 14. This core 10 is arranged with regard to the coil 14 in such a manner that the only, operational, air gap 16 is located Within the interior coil space 18 and substantially in the center of the coil length. The core laminations 12 are stacked tightly at the core ends 20, 2G and along the core legs 22, 22', however, comparatively loosely along the core yoke 24. The lamination stack is secured through clamps 26, 26' of nonferrous material located so to become flush with the carefully finished faces 28, 28' of the core 10. The clamps 26, 26' may be sections of solid, square, tubing or they may be slotted or C-shaped, as shown in FIG. 2. If, for specific applications, a hum-free operation is required in the closed motor condition, the aforementioned sections of solid square tubing will establish the necessary phase angle between line voltage and current and act as shading rings. In fact, this shading ring arrangement, made possible by virtue of the novel core construction, will accomplish the phase displacement in a manner superior compared to that resulting from the conventional shading rings known in the art. The core 10 is disposed, for example, within the space 32 existing between extensions 34 and 34, respectively, integral with the coil body 14. The coil body 14 is equipped with an adequate number of turns 36 of insulated wire of appropriate wire gauge, to suit both the characteristics of the electric power supply and the operational requirements of the electromagnetic motor. The coil leads 38, 33 are attached to the wiring terminals 40, 40, which may be installed on two of the four coil body extensions 34 or 34'. Considering the foreging theoretical treatise on this subject, the coil 14 may be quite short, i.e., commen surate with the length of the air gap 16 between the core faces 28, 2 8'. This in turn facilitates the insertion and installation, respectively, of the iron core assembly 10.

The operation of the described electromagnetic motor is now almost self-explanatory.- If the coil 36 is conneoted, through its terminals 40, 40', to an electric power source regardless of whether it is of the DC. or of the AC. variety, it becomes energized, creates a magnetic field through its interior, induces a magnetic field in the air gap 16 and subsequently through the magnetic circuit, i.e., the iron core 10 disposed partly through the interior space 18 of the coil 14 and closed about the coil 14 by means of the core legs 22, 22 and the core yoke 24, the latter three core portions being integral with the core ends 20, By virtue of the resulting magnetic force, the core faces 28, 28' will attract each other and remain attracted to each other so long as the coil 14 is energized. Upon the opening of the electric circuit to the coil terminals 40, 40' and subsequent deenergization of the coil 14, the spring action of the iron core 10 will become effective and separate the core faces 28, 28' to return the core to the position illustrated in FIG. 1. It is obvious that the loosely stacked yoke portion 24 of the core 10 is primarily responsible for the spring action of the entire core and that no additional mechanical return spring is required. It may be in order to enumerate at this point the other significant and novel features of this electromagnetic motor: (a)'The magnetic circuit comprises only one single part serving as both the traditionally known armature and core having no hinges, abutments or air gaps other than the one required for functional reasons. This results in a magnetic circuit having the least possible magnetic reluctance. (b) The circumstance that the core is laminated, to attain mechanical spring properties, renders the device suitable for both direct and alternating-current operation with substantially equivalent response. (0) Any rough spots or uneven faces on individual laminations having remained or developing on the faces 28, 28' of the core 10 will normally not interfere with the complete closing of the operational air gap 16 because they will seek and align themselves with the corresponding and complementary irregularities on the other core face, by virtue of the substantially freefloating core ends 22, 22. This self-closing property of the only air gap further reduces any remaining magnetic reluctance. (d) In addition to the aforementioned new properties resulting in a considerable reduction of the magnetic reluctances to practically acceptable magnitudes amounting, conversely, to a significant increase of the -magnetic permeability of the entire magnetic circuit, the

now definitely adequate permeability can readily be further improved through the selection of thin strips of grain-oriented, highpermeability materials or alloys for the construction and assembly of the core 10. It now becomes apparent that the electromagnetic motor the construction and operation of which has been fully disclosed in the foregoing, is capable of performing specific, yet interconnected functions within the following operational species.

If the subject electromagnetic motor is used as a genuine motor, one possible construction may comprise the elements shown, schematically, in FIG. 3. The core 10 is disposed with respect to the coil 14 in the manner described in the foregoing, comprising the laminations 12, the clamps 26, 26' and also a shading ring (not shown) if required. A ratchet wheel 42 rotatable about the shaft 44 is arranged in the proximity of the motor assembly. The crank members 46, 46' are attached to the firmlystacked core legs 22, 22 by means of bands 48, 48, and are, at the other end, equipped with pawls 50, 50' pivotal about the axes 52, 52'. Mechanical springs 54, 54, installed on the corresponding legs 46, 46' depress the pawls 50, 50 unto the ratchet wheel 42. An arresting pawl 51, rotatable about the stationary axis 53, and preloaded by a mechanical spring 55, engages the ratchet wheel 42 in a manner to preclude the reversing of the latter. The operation of the motor assembly is self-explanatory from the itemized description of that of the generic electromagnetic motor. It will further become apparent that only one crank-pawl combination 46, 50 may suffice to effect the desired motor action, provided the other, crankless core leg 22 is positioned fixedly with respect to the motor assembly. Conversely, a more continuous or faster ratchet-wheel rotation may be attained if the crank 46 is substituted with a longer crank 46" having an inverted pawl 50 depressed by its mechanical spring 54", as shown in FIG. 4. It is obvious that nu merous additional pawl-ratchet wheel combinations are possible to obtain specific movements of the pawl shaft 44. It also becomes apparent that the motion of the shaft 44 may be utilized for the operation of a countless variety of applications requiring unidirectional, reversible or oscillating propulsion.

.a journal bearing fora pin 72 carrying the lever 74. The

latter is engaged, at its upper extremity 76, by an eye 78 punched into an extension 80 of the clamp 82. This clamp 82 secures like the corresponding clamp 26 the laminations 12 of the core 10 in a previously described fashion. The stationary contacts, i.e., those of the type shown by reference numerals 64 and 68 as well as the movable contacts of the type indicated at 66 are made of electrically conductive yet resilient material such as of beryllium copper or phosphor bronze, and are, at one end, permanently fastened to the interior terminations of the header leads 84, 86, S8, and arranged as presented in FIG. 6. This FIG. 6 shows, in addition thereto, the contact and terminal configuration 90, 92, 94 for the other single-pole, double-throw relay contact set, indicating readily the two-pole, double-throw characteristics of this particular relay embodiment. The two remaining header pins 96, 98 are utilized as coil terminals to the interior portion of which the two coil leads 100, 102 are permanently connected. -To preclude dielectric breakdown and to allow for specific electric cross-over circuits, on insulating board 104 is disposed immediately adjacent to the header 106. This header comprises the required number of pins 84, S6, 88, 90, 92, 94, 96 and 98, imbedded within insulating glass seals 168 which, in turn are fused to both the aforesaid, in this case eight pins and the header 106. The header is off-set at 110 to allow for the seating of the relay enclosure 62 and subsequent sealing as required. If necessary, the core 10 may be secured between the coil body extensions by meansof a clamp 112. The coil wire turns are arranged within the bobbin portion 114 of the coil body 14.

In this case likewise, the operation of the relay, equipped with the generic, electromagnetic motor appears to be self-explanatory. If the coil 114 is connected to an electric power source by means of its terminals 96, 98 it becomes energized magnetizes the core 10, causing attraction among the pole faces. This results in rotation of the lever 74 about the pin 72 and the transfer of the movable contacts such as that indicated at 66 to remain in that position so long as the coil 114 is energized. Upon the de-energization of the coil, the relay parts together with the movable contacts returnto the normal position as it is shown in both FIG. andFIG. 6. It should be noted that the illustrated, but representative relay construction comprises a minimum of parts per se-and of so-called hardware parts such as pins, screws, or nuts, amounting to a considerable increase of operational dependability. In addition thereto, the movable relay parts are physically balanced, resulting in a construction capable of withstanding adverse environmental conditions such as shock, vibration andacceleration. The absence of conventional installation parts allows for miniaturization of this relay construction as well as for economic conversion to any desired large size capable of handling electrical load of considerable magnitude. In the latter case, the relay will be equipped with substantial mounting means rather than with the'plug-in type header base.

A representative solenoid employing the generic electromagnetic motor is portrayed, somewhat schematically, in FIG. 7. One can readily recognize the basic motor comprising the laminated iron core disposed within and about the energizing coil 14 both installed within the enclosure 116, the latter having mounting means 118'. One clamp 26 is provided as in the preceding devices, whereas the otherclamp 120 has an extension 120' toallow for the assembly to a link 122 which, in turn, engages at its opposite end the solenoid plunger 124. The latter has at the other end'provisions 126 for the attachent of members of the device(s) to be actuated by the solenoid. The plunger 124 is guided by the bushing 128 which is integral with the solenoid housing 116. Unless the solenoid is used tooperate two plungers simultaneously, one core leg 22 is positioned with respect to the entire assemblyby means of a rib 130 which may be an integral part of the coil body 14. A lid (not shown) may be installed over the enclosure and fastened thereto with screws mating withthe tapped holes 132. The hole 134 of the bushing 128 may be of round or polygonal cross section. The latter variety will preclude toying. withthe plunger and damage to solenoid parts. The coil leads 136, 136 of the wire turns 36 are brought through an insulating plate 137 to wiring terminals 138, 138 for the attachment of connections to an electrical power source. Whereas the solenoid shown in FIG. 7 is of the pull type, those of the equally popular push type can be readily provided through numerous mechanisms and linkages well known to those familiar with this art. However, the subject solenoid equipped with an electromagnetic motor in accordance with this invention, affords a considerable improvement over prior art in this respect, too. To attain a push-type solenoid utilizing the advantages of the subject electromagnetic motor design it is merely neccessary to exchange the clamp arrangement 26, 120, 120 for that comprising the parts 26, 129" and 123" and to position the core leg 22' fixedly with re spect to the entire solenoid assembly by, means of a coil body extension 130' as shown in FIG. 8. The link 124 will, in this case likewise, complete the transmission to the plunger 122. i

The operation of the solenoid is apparently self-explanatory.

If connected to an electric power source, the sole noid coil 14 will become energized, 'rnagnetize the core '10 resultingin attraction of the core faces 28 and causing a pull or a push action of the plunger 124 depending on the respective mechanism. Upon removal of the electric power, the normal, de-energized position will be re stored as it appears in FIG. 7 or in FIG. 8.

The application of the subject electromagnetic motor as the sensing" and release element of an electric circuit breaker is presented, schematically, in FIG. 9. The gen eric electromagnetic motor comprising the core 10 and the coil 14 is disposed on the circuit-breaker base 140 in such a manner that a core-clamp extension 1420f adequate shape arrests or releases the circuit breakermecha nism. The other core clamp 26 is provided in the usual fashion. Because of the simplicity of the, arbitrarily chosen, circuit-breaker mechanism it may be in order to describe its construction together with its operation: The circuit breaker, shown in the closed or on" position, is" connected to an electric power source by means of its terminals 144, 146. Its internal circuit starting, for example, at the terminal 144, continues, in series, through the conductor 148 to the coil 14 thence through a flexible conductor 150' to the movable circuit-breaker contact 152 and thence to the stationary contact 154 which maybe an integral part of the, other circuit-breaker terminal 146. The coil 14 is designed to carry rated current for an indefinite period of time and the iron core 10 is designed to remain inactive if magnetized with that amount of magnetomotive force created by the coil. However, upon overload and excessive current, respectively, and considering that the core leg 22 is stationary by virtue of the coil body extension 156, the free core leg 22 will be attracted toward the other, move the latch-type core clamp extension 142 with it and release the movable contact 152. This-isfacilitated through a compression spring 158 which causes the movable contact 152 to rotate about a fulcrum 160 formed by an edge of the U-shaped member 162 and that regardless of the attitude of the circuit-breaker handle 164 pivotal about the axis 165. The series circuit is now open which not only results in the elimination of the formerly existing, perhaps dangerous overload condition but also in the de-energization of the sensing element, i.e., of the electromagnetic motor and its return to the position shown in FIG. 9. The tripping further removed the force, transmitted from the movable contact 152 to the member 162 and thence to the handle 164, permitting the handle 164 to rotate to its open or ofi position under the force of a handle return spring (not shown). This allows spring 158 to raise the movable contact 152 now resting on the edge 16%) of member 162, thus preparing the entire circuit-breaker assembly for the next circuitclosing operation. Several conventional circuit-breaker assembly parts well known in the art but not essential for the understanding of the operation of the subject electromagnetic motor in conjunction with a circuit breaker have been omitted not to obstruct the drawing. It should also be noted that the described circuit breaker covers only a single-pole type, whereas it is also readily suitable for the control of multi-pole breakers of any variety or rating.

The electromagnetic motor in accordance with this invention can also serve most advantageously as a pulsing device responding rapidly and loss-free to either externally imposed or self-generated pulses. Whereas the former mode of operation may be self-explanatory, the latter is described in conjunction with a representative construction and circuit utilizing the subject electromagnetic motor, and illustrated, schematically, in FIG. 10.

The iron core 10, disposed within and about the energizing coil 14 is equipped with a plain clamp 26 at one core end which is stationary by virtue of the coil-body extension 171, and with a clamp 170, at the other core end, having an elongated arm 172 carrying, at its extremity, two contact points 174 and 176, capable of mating with the stationary contact points 174' and 176', respectively. If the device and circuit, depicted in FIG. 10, is connected to an electric, D.-C. power source, the coil 14 will be energized, causing magnetization of the core 10, mutual attraction of its faces 28, the closing of contacts 174 and 174- and the short-circuiting and subsequent deenergization of the coil circuit. The spring action of the core will cause the opening of the contacts 174-, 174' and, through recoil action closing of the contacts 176, 176', however, momentarily because the short-circuit across the coil circuit has been opened and the coil circuit restored. Thus, a vibratory action of the electromagnetic motor is established and will continue so long as the circuit shown in FIG. 10 is electrically energized. The particular scheme is used to convert direct current into alternating current with, for example, subsequent transformation.

It is understood that the design, construction and operation of all, the generic electromagnetic motor and the five specific, yet interconnected devices employing the subject electromagnetic motor, were shown and described, respectively, in one but illustrative embodiment each. It is further understood that said electromagnetic motor and the herein disclosed five operational species thereof may be equipped with auxiliary features, such as with partly or wholly magnetically polarized portions to respond to or to cause specific effects. It is also obvious that the de scribed electromagnetic motor and the presented five typical functional species shall not be construed to constitute operative limitations for the application of said electromagnetic motor. Numerous modifications with regard to design, construction and end use appear to be feasible without departing from the spirit of this invention.

What is claimed is:

1. An electromagnetically actuated device comprising a magnetic core formed of a plurality of generally C-shaped strips of flexible magnetizable material nested one inside the other with the strips joined to one another at their ends to form opposing faces of an air gap, the strips being loose one from another in a zone intermediate their ends for independent flexure when the core is flexed to change the size of said air gap, and a coil interlinked with said core to magnetize the core and move said ends relatively toward one another by magnetic attraction against the resistance to bending of the loose portions of said strips in said zone.

2. A device according to claim 1 which further includes mechanism operable in response to the movement of said ends when the core is magnetized.

3. A device according to claim 1 which further includes means for maintaining a region of said core in fixed relation to said coil so that at least one of said ends is movable relative to said coil.

4. A device according to claim 1 wherein said coil jointly embraces said ends and said air gap.

5. A device according to claim 1 wherein said ends of the strips are joined one to another adjacent said air gap by clamping members which embrace the ends.

6. A device according to claim 5 wherein one of said clamping members is of non-magnetic material and also functions as a shading pole.

7. A device according to claim 1 wherein the resistance to bending of said strips provides the sole biasing force for separating said ends when the coil is de-energized.

8. An electromagnetically actuated device comprising a magnetic core formed of a plurality of generally C-shaped strips of flexible magnetizable material nested one inside another and having their respective corresponding end portions joined in fixed relation one to another to define opposing sides of an operational gap in the core, the strips being loose from one another throughout a zone intermediate said end portions for independent fiexure and to resiliently oppose displacement of said end portions relatively toward each other, a coil interlinked with said core and jointly embracing said end portions and said gap, means for holding one region of said core in fixed relation to said coil so at least one of said end portions of the core is free for movement relative to the coil to close said gap against the resistance to bending of the loose portions of said strips in said zone in response to magnetization of the core by said coil, and mechanism 0perated by and in response to such movement of said movable portion of the core.

9. A device according to claim 8 wherein said mechanism operated by said movable portion of the core cornprises means for regulating an electrical circuit.

10. A device according to claim 8 wherein said mechanism operated by said movable portion of the core cornprises a movable electrical terminal adapted for selective positioning by said core to in turn control an electrical circuit.

11. A device according to claim 8 and further comprising a frame member upon which said coil and core are supported, a stationary electrical terminal on said frame, a movable electrical terminal for selective positioning toward and away from said stationary terminal, and means connecting said movable terminal with said movable end portion of the core for effecting said selective positioning of the movable terminal.

12. A device according to claim 8 wherein said mechanism operated by said movable portion of the core comprises a ratchet wheel, a pawl biased against said ratchet wheel, and a link mounted on said movable portion of the core for progressively turning said wheel relative to said pawl.

13. A device according to claim 8 wherein said mechanism operated by said movable portion of the core comprises a link fastened to said movable portion, a ratchet wheel rotatably supported adjacent said link, a pawl pivotally mounted on said link and in driving engagement with said ratchet wheel to rotate said wheel in response to movement of said core end portion when said coil is energized, and means for opposing reverse rotation of said ratchet wheel between successive rotary impulses imparted to the wheel by said pawl.

14. A device according to claim 8 and further comprising a frame member upon which said coil and core are supported, a plunger supported for reciprocation in said frame member, and a link pivotally connected to said frame member and to said movable end portion of the core for reciprocating said plunger in response to movement of said movable end portion of the core.

I 15. A device according to claim 8 wherein said mechanism operated by said movable portion of the core comprises a latch, a link normally biased to a position engaged with said latch, and an electrical terminal engaged with said link when the latter is also engaged by said latch, said latch being responsive to movement of said movable core portion to disengage said link whereby said link is disengaged from said terminal, and means for selectively re-engaging said latch and said link when these parts are disengaged from each other.

16. A device according to claim 15 wherein said link and said latch are electrical conductors in a series circuit with said coil and said terminals.

17. A device according to claim 8 wherein said mechanism operated by said movable port-ion of said core includes a first terminal movable with said core when the 10 coil is energized, a second terminal which said first terminal is adapted to engage when said coil is energized, and a circuit adapted to be made through said first and second terminals to short-circuit the power supply to said coil and thereby de-magnetize said core to effect separation of said first and second terminals.

18. A device according to claim 8 wherein said mecha nism operated by said movable portion of said core includes a first movable terminal adapted for displacement with the core when the coil is energized and de-energized, a pair of stationary terminals the first of which said movable terminal is adapted to engage when said coil is energized and the second of which said movable terminal is adapted to engage upon de-energizing of said coil, 2. first circuit adapted to be made when said first terminal is engaged by said movable terminal to short-circuit the power supply to said coil and thereby demagnetize said core and efiect reopening of said first circuit, and a second circuit adapted to be made when said second terminal is engaged by said movable terminal until said core is again remagnetized.

Field Jan. 1, 1889 Perret Mar, 4, 1902 

